Electroconductive article



United States Patent ELECTROCONDUCTIVEARTICLE Samuel Frank Cox, Arnold, Pa.,- assignor to Pittsburgh Plate Glass Company, Allegheny County, Pa, acol'poration of Pennsylvania I No Drawing. Applicationlllarch 22, 1951, Serial No. 217,080

4 Claims; (Cl. 201-73 This invention relates to improved ceramic or refractory bodies, particularly to transparent ceramic or refractory for United States Letters Patent, Serial No. 762,658,.now

Patent No. 2,614,944, and Serial No. 762,659, now Patent No; 2,648,754, both filed July 22, 1947, by William 0. Lytle. These films or coatings are obtained by spraying plate, window or other glass, while it is heated to a temperature of above 400 F., but below the temperature at which the glass becomes molten, with tin tetrachloride or other tin salts in aqueous solution or in vapor state, in the presence of a reducing agent such as methanol, phenyl hydrazone hydrochloride, or other agents. The films thus obtained areof unknown composition, but appear to" contain a preponderant amount, of theorde'r of 97 to 99%, of' a tin oxide and certain impurities which may include metallic tin, carbon; silicon, and other'impurities, depending u 'n' the'compo'sitioh of the'applied tin containing solution; These filmshave a thickness of about 50 to 80millimicrons, are'trans'parcn't a'ridhave the unusual characteristic of being electroconductive, the particular degree of electroconductivity being dependent, to a large degree, upon the nature of the processof depositing the films. Tin oxide films, which are deposited in accordance with the processes described and claimed in the aforesaid applications'of William O. Lytle, incorporation of thedisclosure of which is 'made "a part hereof by reference, have a resistance below about" 500 ohms per unit square, a specific resistance below about 0.002 ohm centimeters, and a' coeflicient of linear exp-ansion of about 5 to 6X10- per C. between 25 to 475 C.' Further details respecting the productionof these films will be supplied hereinafter.

Although articles having such filmsare usefulin many fields, they have been found to be especially useful as Windshields or viewing closures in automobiles, aircraft, trains and similar automotive vehicles. In such' use" the coating is placed in series with a source of electric potential and is used as a heating eleirie'ntinorder to heat the closure and prevent deposition of ice, fo etc., thereupon. A's disclosed in the Lytle applications, a glass; sheet, usually of plate glass or other flat glass structure (including bent or curved glass structures),- is' provided with conducting metal strips suitable for bus bars. These strips are generally located adjacent the edges of the glass (usually within 0.5 inch of the'edge) and; in the preferred embodiments, are located on opposed marginal edges. For example, in an essentially rectangular viewing closure such as a windshield, two bus bars are applied on;a pair of opposite marginal edges. These metallized strips must be capable of withstanding the temperatures sodium chlorine 2,733,325 Feltented Jan. 31, 1956 and oxidizing conditions of treatment and, therefore, preferably should be'of a ceramic character. Furthermore, they should be capable of glazing or. otherwise forming an adherent, well-bonded coating to the glass. The strips should adhere firmly to the glass sheet, and should have a conductivity atleast 10 to times that of the conductive coating. Generally, the strips are fromabout 0.1 to 1 inch in width. In practice,- it'has been found that the most satisfactory. compositions, for use (preferably gold or silver), and' a vitrifying binder.

In order to avoid production of bus bars which will develop, in use, excessive stresses in the glass, the bus bar preferably should be located on the extreme edge of the glass and the bus bar thickness should not exceed about 0.005 inch and, preferably, should be below about 0.003 inch.

' m an atomizing spray sprayed with an atomized spray of this material for a brief' temperatures of 100 to 125 to cause the'film to After application of the metal busbars to the glass sheet by painting. or other method, the sheet isheated to the temperature at which application of the conductive coating may be effected, for example, above about 400 to 800 F. but below the fusion point of the glass, usually 950 to 1150 F. During this heating operation, the ceramic metal coating becomes glazed and is baked onto the glass so that a firm bond is established between the glassand the metal coating.

When the glass has been heated as above described, for

one or"two minutes, itis withdrawn from the heating.

chamber'and immediately'is sprayed with the coating solution before substantial cooling of the glass sheet can take place: A quantity of the coating solution is placed gun and the heated glass sheet is period, usually of the order of 2m 20 seconds, depending upon the thickness of film to beproduced,-theair pressure imposed upon-the atomizing spray gun, etc. This process results in the production of abase coated with a tin oxide electroconductive film.

Articles produced according to the above description, further details of which will be supplied below, are'suitable for use as viewing closures or windows. Usually they are laminated with a suitable plastic such as polyvinyl butyral to reinforce the glass and provide a so calledsafety glass construction." These closures may be successfully heated by imposing an electric potential across the bus bars, thus using the conductive film as a'resistance element.

Inthe past an unduly'high' number of Windshields or likepanels of the type herein described have failed in use" or test This failure frequently is' manifested by peeling of the electroconductive film from the base after anelectric potential has been imposed across the bus bars be heated, F. or above for a period of time.

In accordance with this invention, it has been found sion of the baseand film upon'heating. For'example', tin oxide films having a coeificient of linear expansion of 5 to 6 10 'per of 25-575 C. when deposited by the methods. described above on a lime-soda glass base having a coefiicient of linear expansion of about 10.5 X10 per C. between 25-500" C. exhibit failure time. When such base and film are so heated, there results'high shear stresses at the interface betweenthe base and film and consequentfailure" of'the panel due to peeling of the film from the base. The coefiicient of linear expansion of the tin oxide films contemplated in the practice of the invention varies from about 5 to 6x10 per C. depending upon the ingredients of the spraying solution employed.

It has been found that substantial reduction in failures in preparing the bus bars, comprise a highly conductive metal powder for example, to to C. between the-temperature range by peeling when heated to' F. or above for a'period of' due to peeling may be effected by use of a base and film which have substantially the same coefficient of linear expansion. It is desirable that the coefficient of linear expansion of the base should not differ more than plus or minus 30 percent from the coefficient of linear expansion of the film, preferably within 10 percent.

Example A typical example of an electroconductive panel embodying the invention is a tin oxide film having a coefiicient of linear expansion of 58x10" per C. between the temperature range of 25-575" C. deposited as described above on a plate glass having a coefficient of linear expansion of 5.89 10- per C. between the temperature range of 25-500 C. Such a glass has the following Polished plates 6" x 6" x 7 made from a glass of the above chemical analysis were heated in a furnace until the temperature of the furnace was indicated to be about 1250" F. and then heated at that temperature for a period of time up to 60 seconds. The heated plates were removed from the furnace and immediately sprayed with a stannic chloride solution composed of the following ingredients:

Stannic chloride grams 20,430

Phenyl hydrazine hydrochloride do 639 An aqueous solution of hydrofluoric acid containing about 48 percent by weight of hydrofluoric acid grams, 134 Distilled water --milliliters-.. 7,056 Dioctyl sodium sulfo-succinate solution do 918 Methanol do 2,250

The spray gun was operated at an air pressure of 50 pounds per square inch and varying quantities, from to 50 cubic centimeters, were sprayed on the plates in order to check the adherence of films of different thicknesses. The adhesion of the tin oxide films to this glass base is excellent and the film exhibits no tendency to peel even when film thickness of as high as 1500 millimicrons are applied to the base.

The invention is particularly applicable for use in connection with transparent tin oxide films. However, the invention is also applicable in connection with other transparent electroconductive films, particularly metal oxide films, wherein the coefficient of linear expansion of the film is substantially the same as that of the refractory base upon which it is deposited. Thus the films herein contemplated may comprise cadmium oxide, antimony oxide, cobalt oxide, zinc oxide, indium oxide, titanium oxide, chromium oxide, platinum oxide, silicon oxide, silver oxide, thallium oxide, etc. which may be prepared using bromide, chloride or acetate of the corresponding metal.

Where viewing closures for vehicles are to be provided, the base for the film normally is ordinary window or lime soda glass. Other refractory materials including borosilicate glass, china, mica, phosphate glass, silicon carbide,

tungsten carbide, porcelain, stone or other refractory composition which melts at temperatures about 1150 to 1350" F. may be provided with electroconductive coatings in the same manner.

Although the present invention has been described with reference to the specific details of certain embodiments thereof, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.v

I claim:

1. A transparent article of manufacture which comprises a transparent glass base having thereon a transparent electroconductive tin oxide film having a coefficient of linear expansion of from 5 to 6X10'- per C., said glass base having a coefficient of linear expansion which does not differ from the coefficient of linear expansion of the film by more than 30 percent.

2. An article of manufacture which comprises a glass base having thereon a transparent electroconductive tin oxide film, said glass base having an analysis substantially as follows:

Percent by weight S102 61.3 B203 13.3 NazO 9.4 Ci: 0.4 ZnO 12.5 S03 0.4 AS205 0.5 A1203 2.2

3. A glass composition having an analysis substantially as follows:

Percent by weigh SiOz 61.3 B203 13.3 NazO 9.4 C12 0.4 ZnO 12.5 SO: 0.4 AS205 0.5 A1203 2.2

4. A transparent article of manufacture which comprises a transparent glass base having thereon a transparent electroconductive tin oxide film having a coefficient of linear expansion of from 5 to 6 l0- per C.,

said base having substantially the same coefiicient of expansion as said film.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Knapp: Alkali-Free Glasses," The Glass Industry, March 1940, pages -6. 

1. A TRANSPARENT ARTICLE OF MANUFACTURE WHICH COMPRISES A TRANSPARENT GLASS BASE HAVING THEREON A TRANSPARENT ELECTROCONDUCTIVE TIN OXIDE FILM HAVING A COEFFICIENT OF LINEAR EXPANSION OF FROM 5 TO 6X10-6 PER *C., SAID GLASS BASE HAVING A COEFFICIENT OF LINEAR EXPANSION WHICH DOES NOT DIFFER FROM THE COEFFICIENT OF LINEAR EXPANSION OF THE FILM BY MORE THAN 30 PERCENT. 